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Old Jun 04, 2003, 05:00 PM
vkmaynard is offline
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How do you test for a bad cell in a pack?


How do you test for a bad cell in a pack without tearing the pack down?

I have several 7XCP2400SCR packs that are getting weak. One I formatted 3 times on my Orbit Pro and now it takes 1800 MHa down from 2400 MHa.

Thanks,

Victor
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Old Jun 04, 2003, 05:10 PM
SheldonYoung is offline
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If you take the shrink wrap off usually the probes from a multimeter will fit between the cells. Put the probes at the positive and negative ends of each cell, one by one, and check that the voltage is good. If you know you're going to work on the pack anyway sometimes it's easier to disassemble the pack to the individual cells and rebuild it from scratch.
Old Jun 04, 2003, 05:29 PM
hoppy is offline
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Good method but battery must be under load for it to work right as an unloaded cell will yield a "good" voltage even tho it's busted

Charge the battery, connect it to a 12 light bulb or some means of discharging the battery, and then measure each cell every couple of minutes. The bad cell will show itself at some point in the discharge process by dropping voltage much quicker than the others. Stop the process when the cell (s) reach 0.9V/cell.

hoppy
Old Jun 04, 2003, 05:41 PM
buzzsaw 46 is offline
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I have used Hoppys method before and it worked for me I had to load the pack to find the week cell.
Old Jun 04, 2003, 05:57 PM
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most of the bad cells i've encounted have shown up on a voltmeter even under no load connected but it's always best to check the indivual cells voltage under some kind of load if possible..... if you don't want to tear off any of the shrink wrap , i connect the meter probes to a pair of sharp sewing needles and "pierce" the wrap at the center of each cells ends to get a good cell reading... the almost invisible wrap just about self seals the little hole after testing .... sometimes if you do find a bad cell (which is usually shorted) i use the same needle piercing method to apply a rather hard indivual cell charge like from an automotive 12 volt battery charger to jolt or burn clear the cells internal short clear.... i've been able to reactivate most dead cells with that method without even removing the shrink wrapper...... kw
Old Jun 04, 2003, 05:59 PM
buzzsaw 46 is offline
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Good info Killer.
Old Jun 04, 2003, 07:02 PM
vkmaynard is offline
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Interesting killer. What causes an "internal short"?

I'll try the suggestions both under load and not underload.

Victor
Old Jun 04, 2003, 07:20 PM
SheldonYoung is offline
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The no-load check is quick and easy and will usually find the dead cell right away. It's those marginal cells that are the pesky ones.
Old Jun 04, 2003, 07:34 PM
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You don't need to access the ends of the cells. Stick your sharp probes through the adjacent sides of the cell wrap. End-to-end you can't do it any other way. Tex.
Old Jun 04, 2003, 09:29 PM
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i don't know if the cell shorts are def mfg, poor QC, internal chemistry contamination or results of the spot welded tabs stresses but the voltage = 0.0 vdc and very low ohms on resistance scales.... seems to show up in new packs during storage before i've had a chance to 1st time charge and use them but after the hard charger pulse hit seem to work just as the normal cells so far........... kw


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